2 
private collection, and also for work on the keys to the genera 
of imagos. We are under special obligation to Dr. P. P. Calvert, 
of Philadelphia, for aid given Mr. Adams in the revision of 
keys and in the determination of doubtful species, and for notes 
on dragon-flies in Illinois made by Mr. Harry Walker at Belvi- 
dere, Mr. Shafer at Mt. Pulaski, and Mr. E. J. Kuegeman at 
Ravenswood and Edgewater. Data relating to collections in 
Illinois have been furnished us by Mr. Maurice Ricker, of Bur- 
lington, ia., and by W. E. Longley, and others, of the Entomo- 
logical Society of Chicago. 
Of the twenty-eight recognized Illinois species of the fami- 
lies of Anisoptera herein treated, we have here described the 
nymphs of twenty-four (six of them for the first time), repre- 
senting all our eleven genera. To these have been added by 
Professor Needham descriptions of ten nymphs of extralimital 
species. Thirty-four nymphs are thus described in all, fourteen 
of them for the first time. 
Much careful study has been given to the preparation of 
the keys. In all cases the linear arrangement is according to_ 
the principles suggested by Comstock, the more generalized 
group or species being followed by the divergent ones in the 
order of the direction and amount of specialization. The de- 
scriptions of the nymphs are drawn up from full-grown exam- 
ples unless otherwise stated. The newly hatched insect quickly 
takes on the form and structure of the full-grown nymph, and 
may usually be recognized while still very young by the char- 
acteristic sculpture and armament of its species. 
